The invention relates to a laminated glazing for use as a head-up display screen. Head-up displays are useful in all types of vehicles, in particular motor vehicles.
Head-up displays display information projected onto a laminated glazing, which is reflected towards the driver or the observer. These systems can especially give information to the vehicle driver without the driver having to divert his gaze from the front field of vision of the vehicle, so as to ensure safety during driving. The driver then sees a virtual image located a certain distance behind the windscreen.
If standard laminated glazing is used for such a system, the driver sees a double image: a first image reflected by the surface of the windscreen oriented into the cockpit, and a second image reflected by the outer surface of the windscreen, these two images being slightly shifted relative to each other. This shift may disrupt the viewing of the information. To overcome this problem, use may be made of a laminated windscreen formed from two sheets of glass and an interlayer made of polyvinyl butyral (PVB), the two outer faces of which are not parallel but wedge-shaped, such that the image projected by a display source and reflected by the face of the windscreen oriented into the cockpit is virtually superimposed on the same image originating from the same source reflected by the face of the windscreen oriented outwards. To produce this wedge-shaped laminated glazing, use is made of an interlayer sheet whose thickness decreases from the upper edge of the glazing to the lower edge.
Moreover, among all the qualities contributing to comfort in modern transportation means such as trains and motor vehicles, silence has become a determining factor.
Acoustic comfort has been improved over several years now, by treating noise, such as noise from the engine, rolling or suspension noise, either at their source or during their propagation through the air or through solids, by means, for example, of absorbent coatings or elastomeric connecting pieces.
The shapes of vehicles have also been modified to improve the penetration in air and to reduce the turbulence, which are themselves sources of noise.
In recent years, attention has been focused on the role that glazing might play in improving acoustic comfort, in particular laminated glazing comprising plastic interlayer films. Laminated glazing also has other advantages, such as elimination of the risk of projection of fragments in the event of sudden breakage, constituting an effraction retarder.
It has been demonstrated that the use of standard plastic films in laminated glazing is unsuitable for improving acoustic comfort. Specific plastic films were then developed, which had damping properties that allow an improvement in the acoustic comfort.
Moreover, in the existing windscreens, the thickness of the glass sheet intended to be turned facing the exterior of the vehicle is generally 2.1 mm and the thickness of the glass sheet intended to be turned facing the interior of the vehicle is generally 1.6 mm. However, the tendency is towards lightening motor vehicles in order to reduce their consumption and the induced discharge of CO2. One means is to propose lighter motor vehicle glazing. One solution for reducing the weight of glazing is to reduce the thickness of the glass sheets. However, this reduction of thickness results in a degradation of the acoustic properties of the laminated glazing.
There is thus a need for a laminated glazing intended to be used as a head-up display screen, the laminated glazing also having vibro-acoustic damping properties and allowing a reduction in the thickness of the glass sheets without degradation of the vibro-acoustic damping properties.